A digital light processor (DLP) is a microelectromechanical system (MEMS) that operates as a fast, reflective digital light switch. A DLP system combines image processing, a memory, a light source, and optics. The DLP may be monolithically fabricated in a complementary metal-oxide-semiconductor (CMOS) process over a conventional CMOS integrated circuit (IC).
A reflective stealth mirror (RSM) is a recent development in DLP systems. As illustrated in FIG. 1, an RSM may comprise one or more movable mirrors 20 and fixed hinges 30 to support the mirrors 20 on a glass substrate 10. Each mirror 20 reflects light in different directions depending on the state of an underlying memory cell.
Two layers of amorphous silicon (a-Si) are typically used during the fabrication of an RSM to fixedly support mirror 20 from the top and bottom. The a-Si layers are removed by etching to release mirror 20 after fabrication of the RSM is completed. Serious metal spiking often occurs at the interface of the mirror sidewalls and the overlying a-Si layer 40, which creates mirror bridges 45 after removal of the a-Si layer 40, as illustrated in FIG. 2. The spiking of the mirror is a major quality issue, as the resulting mirror bridges 45 prevent movement of the mirror 20 during operation of the RSM.
Oxide spacers may be utilized along the sidewalls of the mirror and the overlying a-Si layer to prevent spiking. As illustrated in FIG. 3A, the oxide spacers are conventionally fabricated by depositing a conformal oxide layer 60 over the mirror 20, formed by a bottom oxide layer 21, an intermediate reflective layer 22 and a top oxide layer 23, and anisotropically dry etching the oxide layer 60. If the spacer process is properly controlled, the oxide spacers 60a and 60b will have a height that allows them to completely cover each sidewall of the mirror 20, as illustrated in FIG. 3B. However, the height of the oxide spacers is hard to control using the conventional spacer process due to etching rate variations or unstable endpoint. Hence, the oxide layer 60 may be over-etched thereby resulting in spacers 60a′, 60b′ of insufficient height, which expose the intermediate reflective layer 22. The exposed portions of the reflective layer 22 are where the mirror bridges originate.
Accordingly, a robust spacer fabrication process is needed for manufacturing RSMs, and other MEMS devices, which avoids mirror bridging.